The present invention relates generally to rotatable shaft journalling arrangements and more particularly to a method and apparatus for accurately positioning a rotatable member within a housing.
The assembly of workpieces, such as machinery having rotating parts, frequently requires the precise fitting of antifriction rolling elements such as ball or roller bearings. Tolerances of the manufactured workpiece parts may cause variations in the axial dimensions of the workpiece which may exceed allowable variations for the fitting of bearings therein and therefore often some method of selective fitting or tailoring of a compensating component is required. One method commonly employed is to measure the assembly of components and provide a shim or spacer selected to precisely obtain the desired fit, which may be either a small amount of free end play or clearance, or some prescribed value of a preloading force on the assembly.
In some cases the axial location of the rotating part may be particularly important. For example, in a typical differential axle there is a critical dimension requiring the accurate axial positioning of the differential gear assembly so that the ring gear and pinion gear are in proper close fitting engagement (correct backlash) and the supporting bearings such as tapered roller bearings are in correct axial position for optimum running life. The conventional technique for making such assemblies is a trial and error measuring and fitting of the component parts in order to allow for the customary dimensional tolerances of manufacture of the parts in an economical manner. This selective fitting is usually accomplished by use of thin metal shims which are added or removed after each trial assembly until the correct gear mesh and bearing fit are achieved. Thus, such a trial and error fitting process is, of course, quite time consuming and contributes materially to the overall cost of such a differential axle. This same problem is, of course, present in numerous other rotating devices involving some critical interior dimension on the device rotating member relative to its containing housing.
An early example of an arrangement for preloading ball bearing arrangements in a workpiece is illustrated by U.S. Pat. No. 2,101,130 to Christman. The Christman arrangement provides a deformable or crushable separator element between ball bearing races so that in the assembly of the parts, this separator may compensate for inaccuracies of the workpiece parts. Christman employs a press to deform his spacing element to a preferred load, whereupon the workpiece parts are crimped or otherwise permanently fastened in position. In other words, Christman relatively moves his workpiece parts until a certain preload force is achieved, whereupon the parts are permanently affixed to complete the workpiece.
Another early example of an arrangement for accurately positioning ball bearings having as a stated goal the elimination of trial and error shim removing or inserting techniques of the type discussed above is U.S. Pat. No. 2,911,855 to Opocensky. In this patented device the positioning of the bearing supporting opposed bevel gears in a differential gear assembly is accomplished by employing a deformable non-resilient spacer, positioning the gear to have the appropriate amount of backlash and then fastening the gear in that position. The Opocensky approach is quite limited in the range of classes of mechanisms to which it may be applied and is not, to my knowledge, in widespread commercial use.
In contradistinction improved spacers such as described in my U.S. Pat. Nos. 3,595,588; 3,774,896; 3,900,232; 4,067,585; 4,125,929 and 4,214,465 and in conjunction with the arrangement and method of U.S. Pat. Nos. 3,726,576 and 3,672,019, have met with widespread commercial success. Briefly, my improved annular spacing elements are designed to experience elastic deformation with a relatively linear stress-strain relationship followed by plastic deformation under a relatively constant load or force and when the originally applied deforming force is removed, they again exhibit a relatively linear stress-strain relationship displaced by the amount of plastic deformation from their original stress-strain relationship. Thus attempting to apply the Christman techniques to my spacers would result in either no deformation or a complete crushing. Similarly, attempting to apply the Opecensky techniques to my spacers would result in the bevel gear bearings being subjected to a permanent stress.
As perhaps best illustrated by the aforementioned U.S. Pat. No. 4,214,465 the use of my spacers has until now been generally limited to the use of a single spacer to compensate for dimensional variations of the shaft journals with all of that compensation occuring at one location therefore limiting the use of my spacers to situations where there were no highly critical interior dimensions involved. The first use of the aforementioned U.S. Pat. No. 4,214,465 applied to the establishment of a critical interior dimension as well as the adjustment of the shaft journals was in worm gear speed reducers where the critical dimension of the shaft location can be approached from either direction and the shaft may be moved past the desired location by a small amount and returned to that location provided that the amount of the additional movement equals or is less than the elastic strain of the spacer and bearings. It would be highly desirable to expand the class of machines to which my spacers may be applied to include those having critical interior clearance requirements that can only be approached from one direction. It will become apparent that the present invention may also be used for devices such as worm gear speed reducers and offers the further advantage that the required parts may be simpler and less costly to manufacture. It would be highly desirable to expand the class of machines to which my spacers may be applied to include those having critical interior clearance requirements.